August 30, 2013

Tiger, Leopard Conservation Begins With Protecting Corridors

The most effective landscape-level conservation strategy for the long-term survival of tigers and leopards, according to a new study led by Clemson University conservation geneticists, is to protect the corridors the big cats use for travel between habitat patches.

Clemson University researchers Sandeep Sharma and Trishna Dutta collaborated with colleagues from the Smithsonian Conservation Biology Institute to show how the forest corridors play an essential role in maintaining the flow of genes between the big cat populations in central India. These corridors are paramount for sustaining the genetic variation necessary in maintaining the long-term persistence of the tiger and leopard populations.

The Clemson team analyzed the genes of the estimated 273 tigers and 217 leopards living in four distinct populations in the 17,375-mile Satpura-Maikal region of central India in the first ever gene-flow analysis of these big cats. The researchers used computer modeling to compare contemporary and historical gene flow among the region’s tiger and leopard populations. The results of their study have been published in the Proceedings of the Royal Society B: Biological Sciences and Evolutionary Applications.

The analysis revealed the region’s tiger population divided rapidly twice in history. The first time, the population divided into two clusters about 700 years ago, when vast swathes of central India’s forestland were cleared for agricultural purposes during the early Mughal era. The second division happened around 200 years ago – the population divided into four clusters when the British Empire cut vast tracts of timber to build railroads and ships. A huge increase in tiger hunting also corresponds with this time period.

Currently, the cats live in high densities in the four protected areas, some of which are connected by relatively contiguous corridors of forest. Others, in contrast, are connected by sparse and fragmented corridors.

Nearly 1,500 hair and fecal samples allowed the team to assemble genetic data, which indicates that while the flow of genes between the four tiger and leopard populations has decreased over time, the clusters linked by contiguous forest corridors have maintained a high rate of gene flow. The clusters that have lost connectivity between them have seen the greatest loss in gene flow.

Because of the limited financial and human capital, the study suggests the big cats would be better served by extending conservation efforts beyond source habitats to a larger landscape scale.

“The viability of the forest corridors connecting tiger habitats has a direct affect [sic] on a tigers’ chance of finding an unrelated mate and on the ability of tiger populations to maintain genetic diversity,” Dutta said. “As we know, genetic diversity allows species to survive disease and habitat stress and encourages long-term survival.”

The tiger corridors in central India currently have no legal protection and the Indian Ministry of Environment and Forests recently gave permission for coal mining development in a key forest corridor connecting two of the habitats in the study.

“Mining brings with it many ancillary habitat disruptions," Sharma said. "There are settlements, roads and infrastructure that will have an inevitable impact on the corridors and possibly obstruct the flow of genes between the habitats."

Dramatic human intervention is necessary to save isolated populations of cats from the perils of inbreeding when habitats become islands and a genetic bottleneck occurs.

It sometimes becomes necessary for wildlife biologists to move animals from one population to another. In locations where migratory and breeding patterns have been disrupted, or populations have been cut off, costly man-made corridors have been required.

For example, the Montana Department of Transportation built 41 fish and wildlife crossing structures in 16 miles of wildlife fencing, 39 jump-outs and many wildlife-crossing guards to mitigate the expansion of US 93 and prevent habitat isolation in Northwest Montana.

“Moving animals is inefficient, costly and stressful for the animals. There is also no guarantee that the animals will mate,” Sharma said. “And building manmade corridors is very expensive and logistically challenging. Since we now know that the existing corridors play such a vital role in long-term survival, the best way to enable their success is to take a landscape-scale approach to conservation and protect the corridors from further damage.”